1. Field of the Invention
This invention relates to degradable polymers, and, more particularly, to homogeneous copolymers containing vinyl pyrrolidone (VP) and 2-methylene-1,3-dioxepane (MDO), of defined composition and molecular weight, and to solution and precipitation polymerization processes for making such copolymers.
2. Description of the Prior Art
M. Shtilman et al, in a paper entitled "Biodegradable Polymers of N-Vinyl Pyrrolidone as Potential Carriers for Pharmaceuticals" in the Proceed. Inter. Sump/Control/Rel. Gioact Mater. 21 (1994); Controlled Release Society, IN., pp 746-7, mentioned that copolymers of vinyl pyrrolidone with 2-methylene-1,3-dioxepane would be biodegradable. However, no method of preparation for such copolymers was disclosed although monomer reactivity ratios and IR spectra of the copolymer product were given. Scheme 1 in the paper indicated that the "Reaction of 2-Methylene 1,3-Dioxepane with NVP" proceeded as follows: ##STR1##
The equation was schematic for a 1:1 NVP:MDO (50 mole % VP:50 mole % BMO) copolymer only, and no evidence of biodegradability of such a copolymer was disclosed.
Accordingly, it is an object of this invention to provide copolymers of VP and MDO in defined compositional ranges, molecular weights and Tg values, and to processes for making such copolymers having advantageous properties.
Another object is to provide homogeneous copolymers of VP and MDO in a compositional range of 80-99 mole % and about 1-40 mole % MDO; preferably 85-95 mole % VP and 5-15 mole % MDO, at a K-value of about 30-50, preferably 35-45, and a Tg of about 124-138.degree. C.
Still another object herein is to provide processes for making said homogeneous copolymers of VP and MDO in said composition range and with such advantageous properties.
Another object is to provide a solution polymerization process in isopropyl alcohol as solvent using a free radical initiator to prepare homogeneous copolymers of VP and MDO in the desired compositional range having advantageous physical properties.
Another object is to provide a precipitation polymerization process in heptane solvent with a suitable free radical initiator to prepare homogeneous copolymers of VP and MDO in the desired compositional range.
Among the other objects of the invention is to provide homogeneous copolymers of 60-99 mole t VP and 1-40 mole % MDO, preferably 85-95 mole % VP and 5-15 mole % MDO, which is hydrolytically degradable in aqueous basic or acid solutions.
These and other objects and features of the invention will be made apparent from the following more particular description thereof.